In this art, conventional heading machines, whether of the double heading type or of the rotary type, generally all employ cams for one or more operations, at certain phases of the cycle, to cause the cam follower to cease movement, or to pause, at a certain angle in order to assure synchronization with other operations being performed by the machine. By this means, the cutting operation does not coflict with the process of punching, the punching operation does not conflict with the process of ejecting finished pieces from the die, and so on. Generally, these operations are staggered, with at least one operation being performed after another has been completed. For example, the punching step is executed after the cutting step is completed and the ejecting step is performed after the punching step is completed. For this reason, conventional heading machines must employ one or more cams that have a "pause" phase angle in one or more of the major machine operations, such as cutting, punching, and ejecting.
The major drawbacks of using such cam mechanisms to achieve high speed operation may be generally stated at least by the following three points. First, due to the fact that the cam follower of a cam device will pause and remain motionless for a specific phase angle of the cam surface, the work phase angle of the cam, which may drive the follower to perform a specific operation, will be decreased. As the length of the pause of the pause angle increases, the working phase angle will decrease proportionately. To compensate for this loss of working angle, the remaining working angle must be made steeper, thus causing the rate of acceleration of the follower to be increased. As the acceleration is increased the shock load and stress on both the cam and the follower is increased proportionately. For this reason, malfunctions, damage, and loss may be expected when one is trying to achieve high speed operation.
Second, in order to overcome the high speed stress mentioned above when the cam is driven at high speeds, it is necessary to increase the size of the cam and the cam follower so that their respective load carrying capacities will be increased. However, when the cam occupies more space, more inertia will be produced as the cam revolves. Therefore, cam mechanisms are not well suited to drive heading machine operations in high speed production.
Third, because the cam follower must use a spring in order to insure that the follower is always in contact with the cam surface during high speed operation or when the path of travel is too long, inertial forces on the follower will make it difficult for the follower to return smoothly to the cam surface. Thus, banging, vibration, and other undesirable phenomona, such as localized wear on the cam surface, will result.